Nitrogen in Forks, What am I Doing Wrong?- Mtbr.com
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  1. #1
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    Nitrogen in Forks, What am I Doing Wrong?

    Recently, I used my off-road motorcycle nitrogen shock charging equipment to charge my 2009 Gary Fisher Tassajara Rock Shox Tora SL air forks. I weigh about 230 when geared up, so I put 188 psi according to the gauge. When I took it for a test ride, sag was at about 55%. A couple of days later, a friend with a Fox shock pump let me borrow it. The gauge showed 125 psi. I pumped it up to around 190, and they felt great with a normal amount of sag.

    I had the same issue before on a 2012 Trek Cobia (some sort of Solo Air Rock Shox) (gauge showed one thing and sag was way soft). I have done a couple of motorcycle shocks since, and they were fine.

    It is a lossless chuck (Race Tech brand). Any ideas on what I did incorrectly?

    Thank you for any advice on the charging.

  2. #2
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    55% sag with 188 psi in a fork? Sounds like the air spring is broken, and the main piston seal is worn or desintegrated

  3. #3
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    Well, after using a Fox shock hand pump, it was fine.

    Does it have to be cycled through compression some during charging??

  4. #4
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    Your gauge is off. Also, total waste to charge an air spring with nitrogen!

  5. #5
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    Some shocks have to be cycled to equalize the negative and positive air chambers, if you just pressurize it and go ride, it'll equalize as soon as it sags and then some of your air goes into the negative chamber.
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  6. #6
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    Quote Originally Posted by One Pivot View Post
    Also, total waste to charge an air spring with nitrogen!
    Why?.......Maybe he has more money than you do? Or is there another reason?
    I Pity The Fool That Can't Ride A Bike Without A Dropper!!

  7. #7
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    Quote Originally Posted by tom tom View Post
    Why?.......Maybe he has more money than you do? Or is there another reason?
    Are we financially flexing based on nitrogen purchasing power?

    We dont generate the heat necessary to make wet air matter. For bikes, it's best to use the same shock pump for consistency. You're unlikely to be dragging a nitrogen tank to the trails, but a shock pump easily tosses in a pack for tuning. You might as well start out with the more versatile tool.

  8. #8
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    Quote Originally Posted by Jayem View Post
    Some shocks have to be cycled to equalize the negative and positive air chambers, if you just pressurize it and go ride, it'll equalize as soon as it sags and then some of your air goes into the negative chamber.
    Exactly. When airing up from zero, best to go in reasonable increments, and cycle the fork several times between each "step".

    I use 25 psi increments. I figure this approach really has nothing to lose, and only takes a few extra minutes.
    Whining is not a strategy.

  9. #9
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    Thank you very much for the replies!

    I will cycle / add / cycle / add next time.

    I don't own a bicycle fork / shock pump. The only way I have to get the PSI that high is to use my off-road motorcycle nitrogen tank or wait and borrow a friend's bicycle pump.

  10. #10
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    Quote Originally Posted by One Pivot View Post
    Your gauge is off. Also, total waste to charge an air spring with nitrogen!
    I put nitrogen in everything! Ifp, air springs, tyres......inflatable mattresses......lungs.....

  11. #11
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    There can be such a thing as too much nitrogen...
    Do the math.

  12. #12
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    Quote Originally Posted by JohnnyC7 View Post
    I put nitrogen in everything! Ifp, air springs, tyres......inflatable mattresses......lungs.....
    That's the other reason 80ish percent nitrogen is plenty.

  13. #13
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    https://www.youtube.com/watch?v=DM6_pUE-3Pg

    TOOOOOOOoooooo much nitrogen!!

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